Method for recycling gases used in a lithography tool

ABSTRACT

A system and method are used to isolate a first gas from a second gas using a third gas. A first chamber includes an element that emits light based on a first gas. A second chamber uses the emitted light to perform a process and includes the second gas. A gaslock that couples the first chamber to the second chamber. A gas source supplies a third gas between the first and the second gas in the gaslock, such that the first gas is isolated from the second gas in the gaslock. The first and third gas can be pumped from the first chamber and separated from one another, such that the first gas can be recycled for reuse to form the emitting light.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 10/770,476, filedFeb. 4, 2004 (now U.S. Pat. No. 6,894,293 that issued May 17, 2005),which is a continuation of U.S. Ser. No. 10/300,898, filed Nov. 21, 2002(now U.S. Pat. No. 6,770,895 that issued Aug. 3, 2004), which areincorporated by reference herein in their entireties.

This application is related to U.S. Ser. No. 10/392,793, filed Mar. 20,2003, entitled “Method and Apparatus for Recycling Gases Used in aLithography Tool,” which is incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to lithography systems. Moreparticularly, the present invention relates to recycling light sourcegas in a lithography tool.

2. Background Art

Lithography is a process used to create features (e.g., devices) on asurface of one or more substrates (e.g., semiconductor wafers, or thelike). Substrates can include those used in the manufacture of flatpanel displays, circuit boards, various integrated circuits, and thelike. During lithography, the substrate is positioned on a substratestage and is exposed to an image projected onto the surface of thesubstrate. The image is formed by an exposure system. The exposuresystem includes a light source, optics, and a reticle (e.g., a mask)having a pattern used to form the image. The reticle is generallylocated between the light source and the substrate. In extremeultraviolet (EUV) or electron beam systems, the light source is housedin a light source vacuum chamber and the exposure system and substrateare housed in an optics vacuum chamber. The light source chamber and theoptical chamber can be coupled via a gaslock.

In a lithography, feature (e.g., device) size is based on a wavelengthof the light source. To produce integrated circuits with a relativelyhigh density of devices, which allows for higher operating speeds, it isdesirable to image relatively small features. To produce these smallfeatures, a light source is needed that emits short wavelengths of light(e.g., around 13 nm). This radiation is called EUV light, which isproduced by plasma sources, discharge sources, synchrotron radiationfrom electron storage rings, or the like.

In some systems, EUV light is created by utilizing a discharge plasmalight source. This type of light source uses a gas or target materialwhich is ionized to create the plasma. For example, the plasma-basedlight source can use a gas such as xenon. Then, the plasma is formed byan electrical discharge. Typically, the EUV radiation can be in therange of 13–14 nm. In other systems, EUV radiation is produced fromlaser produced plasma sources. In the laser produced plasma source, ajet of material (e.g., xenon, clustered xenon, water droplets, iceparticles, lithium, tin vapor, etc.) can be ejected from a nozzle. Alaser is spaced from the nozzle and emits a pulse that irradiates thejet to create the plasma. This plasma subsequently emits EUV radiation.

In order to produce a relatively large amount EUV light, a concentrationof xenon must be relatively high where the plasma is being created(e.g., in the light source chamber). This produces a pressure that istoo high for efficient transmission of the EUV light through theremainder of the system (e.g., the optics chamber). As a result, thepath in which the EUV light travels must be evacuated. Usually, largevacuum pumps are used to remove the source gas as quickly as possibleafter it has performed its function of creating the EUV light.Unfortunately, at high machine throughput, a relatively large amount ofsource gas is pumped away. The cost of source gas such as xenon issubstantial, and will result in a higher per wafer cost unless thesource gas is recycled. Recycling the source gas is complicated by theinclusion of other gases being emitted from the remainder of the EUVlithography tool that mix with the source gas.

Accordingly, in some lithography tools the source gas is kept separatefrom gases in the remainder of the lithography tool by a very thinmembrane. The membrane also removes unwanted radiation by functioning asa spectral filter. However, lithography tools having high throughput andhigh light intensity may not be able to have the membrane due to highthermal loading, which destroys the membrane. Thermal calculations showthat the membrane would have to have a very large surface area to avoidvaporizing when the light source is turned on. A large surface,extremely thin membrane cannot be used in practice, even if they couldbe manufactured, due to their fragile nature. If the membrane isremoved, a barrier between the source chamber and the rest of the toolis gone and gas mixing occurs, making the source gas recycling taskextremely challenging, and in some cases completely impractical.

Therefore, what is needed is a method and apparatus of isolating gas ina light source chamber from gases being emitted from the remainder of alithography tool to allow the gas in the source chamber to beefficiently recycled.

BRIEF SUMMARY OF THE INVENTION

An embodiment of the present invention provides a system including afirst chamber including an element that emits light based on a first gasand a second chamber that uses the emitted light to perform a processand that includes a second gas. The system also includes a gaslock thatcouples the first chamber to the second chamber. The system furtherincludes a gas source that supplies a third gas between the first andthe second gas in the gaslock, such that the first gas is isolated fromthe second gas by the gaslock.

Another embodiment of the present invention provides a system, includinga light source chamber having a first gas, an optics chamber having asecond gas, a first means for coupling the light source chamber to theoptics chamber, and a second means for passing a third gas through thefirst means to isolate the first gas from the second gas.

A further embodiment of the present invention provides a methodincluding (a) producing light with a first gas, (b) processing opticswith a second gas, and (c) separating the first gas from the second gaswith a third gas that flows between them.

In one aspect of the embodiment, the first and third gas are pumped fromthe first chamber, the first gas is separated from the third gas, suchthat the first gas can be recycled for reuse.

Further embodiments, features, and advantages of the present inventions,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 shows a lithographic system, according to embodiments of thepresent invention.

FIG. 2 shows a lithographic system, according to embodiments of thepresent invention.

FIG. 3 shows gas flow through a gaslock in the lithographic system ofFIG. 2.

FIG. 4 shows a flowchart depicting a method according to an embodimentof the present invention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements. Additionally, the left-mostdigit(s) of a reference number identifies the drawing in which thereference number first appears.

DETAILED DESCRIPTION OF THE INVENTION

While specific configurations and arrangements are discussed, it shouldbe understood that this is done for illustrative purposes only. A personskilled in the pertinent art will recognize that other configurationsand arrangements can be used without departing from the spirit and scopeof the present invention. It will be apparent to a person skilled in thepertinent art that this invention can also be employed in a variety ofother applications.

FIG. 1 show a system 100 for forming a pattern on a wafer or substrate102 according to embodiments of the present invention. A light source104 (e.g., an EUV light source) emits a light beam that passes through abeam conditioner 106 and illumination optics 108 before being reflectedfrom a reticle or mask 110. After reflecting from reticle or mask 110,the light beam passes through projection optics 112, which is used totransfer a pattern from a surface 114 of reticle or mask 110 onto asurface 116 of wafer or substrate 102. Other arrangements of theseelements can be used without departing from the spirit and scope of thepresent invention.

FIG. 2 shows details of an exemplary system 200 according to anembodiment of the present invention. System 200 includes a first chamber(e.g., a light source chamber or vacuum light source chamber) 202 andsecond chamber (e.g., an optics chamber or optics vacuum chamber) 204.Second chamber 204 can include one or more of: a beam conditioner,illumination optics, a reticle, projection optics, and/or a wafer. Firstchamber 202 and second chamber 204 can be coupled via a gaslock 206.Basically, a gaslock is an area that allows first and second gases toremain isolated from one another based on a third gas flowing betweenthem (e.g., forming a barrier between them), which suppresses: mixing ofthe first and second gas or transfer of material from first chamber 202to second chamber 204, or vice versa.

When a plasma-based light source is housed in first chamber 202, a firstgas or other material 208 (e.g., xenon, lithium vapor, tin, krypton,water vapor, a metal target, or the like) is ionized to create theplasma, as discussed above. First gas 208 is only supplied to firstchamber 202 during a time when light is being generated. At other times(e.g., during stand-by, idle, maintenance, or other modes), firstchamber 202 is substantially in a vacuum state. Second chamber 204includes a second gas (e.g., a process gases, such as helium, argon,hydrogen, nitrogen, or the like) 210. Second gas 210 can be used toreduce contamination in second chamber 204 and protect lithography toolmirrors located in second chamber 204. Similarly to first gas 208,second gas 210 is only supplied to second chamber 204 during a time whencleaning or protection is required. At other times, second chamber 204is substantially in a vacuum state. A vacuum state is needed in chambers202 and 204 to allow EUV light to be transmitted because EUV light has asubstantially short wavelength (e.g., 13–14 nm), so it cannot readilypass through any gas, which usually absorbs it. Thus, a vacuum stateallows this wavelength of light to easily travel to and through secondchamber 204.

FIG. 3 illustrates an interaction of gases in gas lock 206 according toembodiments of the present invention. First and second gases 208 and 210are supplied to first and second chambers 202 and 204 via first andsecond gas sources 300 and 302. A third gas 304 (e.g., helium, neon,nitrogen, etc.) is passed through an inlet 306 in gas lock 206 from agas source (not shown). In an embodiment, third gas 304 can becontinuously passed through an inlet in gas lock 206. Third gas 304should be chosen so that it is easily stripped out of first gas 208during a recycling device stage (e.g., a purifying and recycling stage),as discussed below. By purifying and recycling first gas 208, system 200of the present invention reduces costs over conventional systems thatmust discard the first gas 208 after its initial use because it mixeswith second gas 210. The discarding of first gas 208 makes upsubstantial amount of the running expense of the tool.

The flow of third gas 304 forces molecules of first gas 208 to travel ina direction of arrow 308. Similarly, the flow of third gas 304 forcesmolecules of second gas 210 to travel in a direction of arrow 310. Thus,the flow of third gas 304 isolates first gas 208 from the second gas210. In an embodiment, first gas 208 and third gas 304 are pumped fromfirst chamber 202 using a pump (e.g., a vacuum pump) 312. Then, firstgas 208 is separated from third gas 304 in recycling device 314, suchthat first gas 208 can be reused to form the emitted light. For example,third gas 304 can be chosen to have a freezing point (e.g., −60° C.),which is substantially above a freezing point (e.g., −200° C.) of firstgas 208. Then, third gas 304 is frozen, separated from first gas 208,and removed from recycling device 314. In various embodiments, first gas208 can either be reused directly from recycling device 314 ortransmitted to gas source 300.

It is to be appreciated that in various embodiments third gas 304 can bereused after exiting recycling device 314 or it can be discarded. It isalso to be appreciated that although pump 312 and recycling device 314are shown coupled directly to a top of first chamber 202, either one orboth of pump 312 and recycling device 314 can be indirectly coupled tofirst chamber 202 and/or they can be positioned anywhere with respect tofirst chamber 202. Also, although not shown, it is to be appreciatedthat second gas 210 can also be recycled using similar or functionallysimilar devices, as is known in the art.

FIG. 4 shows a flowchart depicting a method 400 according to anembodiment of the present invention. At step 402, light (e.g., extremeultraviolet light) is produced with a first gas (e.g., xenon, lithiumvapor, tin, krypton, and water vapor). At step 404, optics are processedwith a second gas (e.g., helium, argon, hydrogen, and nitrogen). At step404, the first gas is separated (e.g., isolated) from the second gaswith a third gas (e.g., helium, neon, and nitrogen. that flows betweenthem.

CONCLUSION

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

1. A method, comprising: (a) receiving in a gas lock a first gas from afirst portion of a lithography tool; (b) receiving in the gas lock asecond gas from a second portion of the lithography tool; (c) directinga third gas between the received first gas and the received second gasto isolate the first gas from the second gas in the gas lock; (d)removing the first and third gas from the gas lock; (e) separating thefirst from the third gas; and (f) recycling the first gas.
 2. The methodof claim 1, wherein step (a) comprises: using one of xenon, lithiumvapor, tin, krypton, and water vapor as the first gas.
 3. The method ofclaim 1, wherein step (b) comprises: using one of helium, argon,hydrogen, and nitrogen as the second gas.
 4. The method of claim 1,wherein step (c) comprises: using one of helium, neon, and nitrogen asthe third gas.
 5. The method of claim 1, wherein: the first gas isreceived at the gas lock from a light source chamber; and the second gasis received at the gas lock from an optics chamber.
 6. The method ofclaim 5, further comprising: using the first gas to generate a plasmaillumination in the light source chamber.
 7. The method of claim 6,wherein the plasma illumination is produced having wavelengths in anextreme ultra violet spectrum.